userfaultfd/selftests: always dump something in modes

Patch series "userfaultfd: selftests: Small fixes".

Some very trivial fixes that I kept locally to userfaultfd selftest
program.

This patch (of 3):

BOUNCE_POLL is a special bit that if cleared it means "READ" instead.
Dump that too otherwise we'll see tests with empty modes.

Link: https://lkml.kernel.org/r/20201208024709.7701-1-peterx@redhat.com
Link: https://lkml.kernel.org/r/20201208024709.7701-2-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/vm/userfaultfd.c

@@ -1291,6 +1291,8 @@ static int userfaultfd_stress(void)
 			printf(" ver");
 		if (bounces & BOUNCE_POLL)
 			printf(" poll");
+		else
+			printf(" read");
 		printf(", ");
 		fflush(stdout);